In the existing techniques, e.g., the train radioactive materials monitor YANTAR-1/2ZH of Aspect Corporation, monitoring of gamma rays or/and neutron rays is (or are) realized by detecting the abnormal variation of the system's count rate caused by the gamma rays or/and neutron rays radiated by the radioactive materials. However, this kind of device can not provide position information on where the radioactive materials are located. Once it has been determined that a vehicle is loaded with radioactive material(s), an inspection of the vehicle may be required in order to locate the radio active material. In practice, some containers under monitoring are as long as 18 meters (trains are longer), or can have multiple sections or storage compartments. Thus, individual inspection of the vehicles can require significant time and/or human resources.